Start Kyrie/Smart/Tatum/Horford/Baynes.
Have Smart guard Giannis on the perimeter. Use Smart to harass/chase/body/deny Giannis the ball and take charges. Horford/Baynes are there to help/switch if/when Giannis gets into the paint. The goal is to keep Giannis from going downhill and keep him out of rhythm and frustrate him. It seems to me, with Horford guarding Giannis he gives Giannis space to catch on the perimeter and then tries to body him/contain him as he drives, unfortunately this lets Giannis get that downhill speed going which makes him harder to stop, so try to cut that off to begin with. And I'll live with whatever Lopez/Mirotic produce with Horford/Baynes helping off them.
Baynes is averaging 7mpg in this series, so don't be afraid to have him use all 6 fouls making Giannis earn every point in the paint.
Moving Brown/Morris to the bench will hopefully provide some bench scoring (bench only hit 3 and 4 FG the last 2 games, as well as it staggers the guys the C's can throw at Giannis.
Or, since 1st half doesn't seem to be a problem (C's are +2, -4, +1, +2 at the half), continue to do normal game plan 1st half and the be ready to roll out something completely different 2nd half, especially for that 3rd quarter! I don't care if that means putting in Wannamaker, Yabusele, and Williams to start the 2nd half. Anything to throw the Bucks off. Ya there's probably a reason I'm not a head coach lol.